Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenue				$ 5,000
Operating expenses:
Research and development	$ 4,584	$ 16,925	$ 11,102	33,072
General and administrative	4,366	3,682	7,953	7,626
Total operating expenses	8,950	20,607	19,055	40,698
Loss from operations	(8,950)	(20,607)	(19,055)	(35,698)
Interest income	54	297	261	654
Interest expense	(6)		(9)
Other income, net	9	292	32	608
Net loss	$ (8,893)	$ (20,018)	$ (18,771)	$ (34,436)
Net loss per share—basic and diluted	$ (0.17)	$ (0.39)	$ (0.36)	$ (0.67)
Weighted average common shares outstanding—basic and diluted	52,147,656	51,097,456	52,147,145	51,037,514
Other comprehensive income:
Unrealized gain (loss) on investments	$ (43)	$ 15	$ (7)	$ 32
Comprehensive loss	$ (8,936)	$ (20,003)	$ (18,778)	$ (34,404)